Overspeed device



OVERSPEED DEVICE Filed Dec. 5, 1950 Figl.

TO CONTROL ClRCUlT Inventor- Carl H.Er-icson,

His Attorney.

United States harem OVERSPEED DEVHCE Carl H. Ericson, Buffalo, N. Y,assignor to General Electric Company, a corporation of New YorkApplication December 5, 1950, Serial No. 199,282

9 Claims. (Cl. 123-148) This invention relates to speed responsivedevices, and more particularly to electrically actuated overspeeddevices.

It is an object of the invention to provide an improved and simplifiedspeed responsive device for a machine which provides a pulsating voltagesubstantially proportional to its speed or for any machine which iscapable of producing a pulsating voltage because it rotates, oscillates,reciprocates, vibrates or the like.

A more specific object of my invention is the provision of anelectrically actuated overspeed device which need not be connected tothe shaft of the machine which is to be protected.

Other objects and advantages of the invention will be apparent from thedetailed description given hereinafter, while the scope of the inventionis defined in the appended claims.

In carrying out my invention in one form, I provide an overspeed devicehaving two impedances serially connected to a source of pulsatingelectrical potential whose frequency is proportional to the speed of themachine to be protected. One of the impedances is a capacitor, theimpedance of which varies inversely with frequency, and the other is aresistor, the impedance of which is substantially unaffected byfrequency, with the former being of considerably larger impedance thanthe latter over the normal operating range so that the amplitude of thecurrent through the series circuit is approximately proportional to thefrequency. A voltage responsive device connected in shunt with theresistance is arranged to operate when the current through theresistance reaches a value sufficient to produce a predetermined voltagedrop thereacros-s.

For a clearer and more complete understanding of my invention, referenceshould be had to the accompanying drawing in which Fig. l is a schematicdiagram of one preferred embodiment thereof, while Fig. 2 depictsschematically an embodiment of more general adaptability than Fig. 1.

Referring to Fig. l of the drawing, there is shown a form of theinvention adaptable for use with a machine, such as an automobile enginefor example, which provides a pulsating voltage proportional to itsspeed. In this embodiment the overspeed device is actuated by thepulsating potential produced by the engines ignition system.

There is shown in Fig. l a portion of a conventional automobile engineignition system. The battery, which may be a six volt battery forexample, is designated by the numeral 10 and one terminal of thebattery, which may be the negative terminal, is grounded at 11. Aswitch, which maybe a conventional automobile ignition switch or othersimilar switch, is shown at 12, while the primary circuit breaker whichperiodically interrupts the primary ignition circuit at a frequencyproportional to the speed of the engine to produce a pulsating voltagewhich is also proportional in frequency to the speed of the engine, isrepresented schematically by switch 13.

This circuit breaker has acondenser connected in shunt therewith in theconventional manner and this condenser is designated by the numeral 14.The primary circuit interrupter is connected to the primary winding 15of an ignition transformer, and winding 15 is grounded at 16. Thesecondary winding of the ignition transformer, the distributor and thespark plugs are not shown in order to simplify the drawing, these partsof the ignition system not being necessary to an explanation of theinvention.

There is connected to the ungrounded side of the ignition transformerprimary winding, in a suitable manner such as by a spring clip 17, aseries circuit comprising a capacitor 18 and an adjustable potentiometerresistance 19 having a slider 19a. The negative terminal of the resistoris grounded at 20. Connected in shunt between the slider 1% of theadjustable resistance and the grounded terminal is a voltage responsivedevice. This is illustrated as a dArsonval type contact makingmicroammeter 21 having an operating coil Zia. This coil is connected inshunt with the effective portion of resistor 19 through a bridge typerectifier 21c which is preferably an integral part of instrument 21. Thecontact making microammeter is provided with contacts Zlb which areconnected to shunt the coil of a solenoid 2.2 when the contacts close.

The solenoid 22 operates a pair of switches 23 and24 and forms oneelement of a typical control circuit which may be used with the presentinvention in the testing of an automobile engine. This control circuitalso includes a momentary contact push button switch 25 and a resistor26. Current for the operation of the control circuits may be supplied byany conventional source, and in this instance is. indicated as beingsupplied at volts 60 cycles by conductors 2'7 and 28. The closing ofpush button switch 2.5 energizes solenoid 22 through resistor 26 andcloses switches 23 and 24. The closing of switch 23 completes a hold-incircuit for solenoid 2.2, permitting the release of switch 25 withoutdeenerg'izing the solenoid. The closing of switch 24 completes :theignition circuit of the engine, as is subsequently discussed in greaterdetail in connection with the operation of Fig. 1.

In accordance with my invention, the impedance of capacitor i8 ispreferably considerably greater than the impedance of resistor 19 overthe frequency range which is to be utilized. Inone typical device usedfor testing six cylinder, 4 cycle automobile engines operating between500 and 4,000 R. P. M., a capacitor having value of .l microfarad wasused for element 13 while a resistance having a value of 10,000 ohms wasused for element 19; With this combination, a contact makingmicroammeter having a range of 0-200 microamperes was used aselement-Zl.

This arrangement resulted in a capacitor impedance which varied fromapproximately 65,000 ohms at the lower speed of 500 R. P. M. toapproximately 8,000 ohms at 4,000 R. P. M. engine speed. The impedanceof the capacitor in the upper portion of the operating range'thus wasslightly less than the total impedance of the resistor. Nevertheless,the overspeed device operated entirely satisfactorily.

In general, it is desirable to have the impedance of the capacitorgreater than the impedance of the resistor over the entire frequencyrange. The greater the ratio by which the capacitor impedance exceedsthe resistor impedance the more linear is the variation of the currentthrough the resistor with variations in frequency. Greater linearity inthe resistor current produces greater linearity in voltage drop acrossthe resistor, and makes it possible toobtain satisfactory results fromthe overspeed device withavoltage responsive device of minimum accuracyand cost.

It will be understood, of course, that other voltage responsive devices,such as solenoid operated contactors, relays, and other similar devicesfor example, may be used instead of the contact making microammeterillustrated without departing from my invention. It will be readilyunderstood also that a potentiometer resistor, such as is illustrated byelement 19 on the drawing, is not an essential part of the invention,and that a less expensive fixed resistor can be substituted in manycases when extreme accuracy is not required.

With the connection illustrated in Fig. 1, the signal presented to theprimary of the ignition coil is essentially a square wave of constantamplitude and variable frequency, the value of the frequency dependingupon the speed of the engine. Therefore, if the impedance of 13 isappreciably greater than the impedance of 19 at the highest frequencyused, the amplitude of the current flowing through thecapacitance-resistance series circuit is approximately proportional tothe frequency and, therefore, approximately proportional to the speed ofthe engine. This is because the impedance of capacitor 18 variesinversely with the frequency, and this impedance being larger than theimpedance of resistor 19 predominates in determining the value ofcurrent in the series circuit.

The circuit illustrated in Fig. l, as previously stated, may be utilizedto provide overspeed protection for an engine which is to be tested. Inoperation, ignition switch 12 is first closed and then push buttonswitch 25 is operated. Closing switch 25 energizes the coil of solenoid22 through resistor 26 and closes switches 23 and 24. The closing ofswitch 23 provides a hold-in circuit for solenoid 22 when momentarycontact switch 25 is released. The closing of switch 24 completes theignition circuit of the engine from the battery through the primarywinding of the ignition coil and permits operation of the engine atvarious speeds in the usual manner. To adjust the microammeter 21, theengine is set at the desired maximum safe speed and resistance 19 isthen adjusted until, by visual inspection, it is determined that thecontacts of microammeter 21 are just about to close. Thus, no accuratecalibration of the overspeed device is necessary.

During subsequent tests of the engine, if it should run away for anyreason, such as a coupling breaking between the engine and a dynamometerbeing used to load it for example, the frequency of the ignition circuitwould increase and thereby increase the current through the seriescircuit formed by capacitor 18 and resistor 19. When the voltage dropacross the effective portion of the latter increases suificiently toprovide enough current to operate microammeter 21 and close contacts21b, the engine is immediately shut down. The closing of contacts 21bshunts the coil of solenoid 22 causing the solenoid to drop out and openswitches 23 and 24. The latter opens the ignition circuit of the enginewhile the former opens the control circuit. The engine will then remaininoperative until the control circuit again is actuated by depressingpush button switch 25.

From the foregoing it will be apparent that this invention provides anoverspeed protective device which need not be connected to the shaft ofthe machine, and which makes unnecessary any of the usual electrical,liquid, centrifugal or other tachometer devices. It will be appreciatedthat it is of great advantage to have an overspeed protective devicewhich need not be connected to the shaft of the machine because of theinaccessibility of the shafts of many machines, such as the crank shaftsof automobile engines for example.

In Fig. 2 of the drawing, there is illustrated an embodiment of theinvention of more general adaptability than Fig. 1. in this figure, likeparts bear like numerals with the corresponding parts in Fig. 1. Theform of the invention illustrated in Fig. 2, may be used for any machinethat rotates, reciprocates, oscillates or vibrates, or has any periodicmotion by means of which it is capable of producing an alternating orpulsating voltage.

A portion of such a machine, which may, for example,

be a portion of a piston rod, valve arm, cam, rocker arm or other movingpart is illustrated at 29 in Fig. 2. The two arrows extending up anddown from element 29 indicate schematically that this point on themachine has a periodic motion so that a movable contact 30 which isconnected to point 29 and pivoted about a point 31 contacts alternatelyfixed contacts 32 and 33.

In Fig. 2, two sources of potential, such as a pair of batteries ltiaand 1652, are used, With two terminals of opposite polarity joined toform a midpoint and with the lower terminal of resistance 19 connectedto this midpoint. The other terminals of the batteries are connected tocontacts 32 and 33 respectively whereby an alternating voltage resultsfrom the alternate engagement of movable contact member 38 with fixedcontact members 32 and 33. This alternating voltage, impressed on theseries circuit including capacitor 13 and resistor 19, operates in thesame manner as described for Fig. 1; that is, the amplitude of thecurrent through the series circuit varies approximately proportionallywith the frequency of the alternating potential. The voltage responsivedevice 21 is then set so that when the current through the effectiveportion of resistance 19 reaches a certain predetermined valuecorresponding to a selected speed of the machine being protected, thedevice 21. operates to close its contacts and energize a control circuitto discontinue operation of the machine or perform any other desiredoperation. Thus, a speed responsive device is provided for any machinehaving a periodic motion which can be translated into an alternating orpulsating potential.

While I have illustrated and described in detail certain preferredembodiments of my invention, many modifications thereof may be made bythose skilled in the art, and it should be understood, therefore, that Iintend to cover by the appended claims all such modifications which fallwithin the true spirit and scope of my invention.

What i claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A control system for a machine comprising means for deriving apulsating voltage having a frequency proportional to the speed of themachine comprising a source of direct voltage and a circuit suppliedfrom said source including make and break contacts opened and closed inresponse to the speed of the machine, a first impedance whose valuevaries with frequency connected to be energized by said voltage, asecond impedance whose value is relatively unaffected by frequencyconnected to be energized in series with said first impedance, saidfirst impedance being larger than said second impedance over at leastmost of the operating range of said speed responsive device whereby theamplitude of the current in said series circuit is responsiveprincipally to the value of said first impedance, and a voltageresponsive device connected in shunt with said second impedance andarranged to perform a control operation in connection with said machinewhen the voltage drop across said second impedance reaches apredetermined value corresponding to a selected speed of said machine.

2. A control system for a machine comprising means for deriving apulsating voltage having a frequency substantially proportionalcomprising a source of direct voltage and a circuit supplied from saidsource including make and break contacts opened and closed in responseto the speed of a machine, a capacitor of relatively large impedance anda resistor of relatively small impedance serially connected and arrangedto be energized by said pulsating voltage, and a voltage responsivedevice connected in shunt with said resistor and arranged to perform acontrol operation in connection with said machine when the voltage dropacross said resistor reaches a predetermined value.

3. A speed responsive device for an engine having an ignition circuitproviding a pulsating voltage whose frequency is substantiallyproportional to the speed of the engine, comprising a first impedanceWhose value varies inversely with frequency connected to be energized bysaid ignition voltage, a second impedance Whose value is substantiallyunaffected by frequency connected in series with first impedance, saidfirst impedance being appreciably larger than said second impedanceWhereby the amplitude of the current in said series circuit isapproximately proportional to the speed of said engine, and a voltageresponsive device connected in shunt with said second impedance andarranged to perform a control operation in connection with said enginewhen the voltage drop across said second impedance increases to apredetermined value corresponding to a selected speed of said engine.

4. A speed responsive device for an engine having an ignition circuitproviding a pulsating voltage whose frequency is substantiallyproportional to the speed of the engine, comprising a capacitor ofrelatively large impedance and a resistor of relatively small impedanceserially connected and arranged to be energized by said ignitionvoltage, and a voltage responsive device connected in shunt with saidresistance and arranged to perform a control operation in connectionwith said engine when the voltage drop across said resistor increases toa predetermined value corresponding to a selected speed of said engine.

5. A speed responsive device for a machine having a periodically movingpart whose period is proportional to the speed of the machinecomprising, movable contact means connected to be operated by saidmoving part, fixed contact means associated with said movable contactmeans and arranged to be periodically engaged thereby at a frequencycorresponding to the movement of said moving part, connections forapplying an electrical potential between said fixed and movable contactmeans whereby a pulsating voltage having a frequency proportional to thespeed of said machine is provided by the periodic engagement of saidfixed and movable contact means, a capacitor of relatively largeimpedance and a resistor of relatively small impedance connected inseries and arranged to be energized by said pulsating voltage, and avoltage responsive device connected in shunt with said resistor andarranged to perform a control operation in connection with said machinewhen the voltage drop across said resistor increases to a predeterminedportion of the total voltage drop across the capacitor and the resistor.

6. A speed responsive device for a machine having a periodically movingpart Whose motion is responsive to the speed of said machine, comprisingmovable contact means connected to said moving part and arranged to bemoved by the motion thereof, fixed contact means associated with saidmovable contact means and arranged for periodic engagement with saidmovable contact means at a frequency corresponding to the period ofmotion of said moving part, electrical connections for applying anelectrical potential between said fixed and movable contact meanswhereby a pulsating voltage is produced having a frequency correspondingto the frequency of engagement of said contacts, a first impedance Whosevalue varies with frequency connected to be energized by said pulsatingvoltage, a second impedance whose value is substantially unaffected byfrequency connected in series with first impedance, said first impedancebeing considerably larger than said second impedance whereby theamplitude of the current in said series circuit is determinedprincipally by the value of said first impedance, and a voltageresponsive device connected in shunt with said second impedance andarranged to perform a control operation in connection with said machinewhen the voltage drop across said second impedance reaches apredetermined value corresponding to a selected speed of said machine.

7. An overspeed device for a machine having a periodically moving partwhose frequency is proportional to the speed of the machine, comprisinga pivoted movable contact member connected to said moving part, a pairof fixed contact members oppositely disposed in operative relation withsaid movable contact member and arranged to be contacted alternately bysaid movable contact memher, a source of unidirectional potentialconnected to said fixed contact members, said source of potential havinga point of intermediate potential connected to said movable contactmember whereby an alternating voltage is produced having a frequencyproportional to the speed of said machine, a capacitor and a resistorserially connected in the circuit between said intermediate point andsaid movable contact, said capacitor having a considerably largerimpedance than said resistor whereby the amplitude of the currentthrough said series circuit is approximately proportional to theimpedance of said capacitor, and a contact making voltage responsivedevice connected in shunt with at least a portion of said resistor, saidvoltage responsive device being arranged to close its contacts upon theoccurrence of a predetermined amplitude of current in said resistorproducing a predetermined voltage drop thereacross.

8. A speed responsive device for an engine having an ignition circuitproviding a pulsating voltage Whose frequency is proportional to thespeed of the engine, comprising a capacitor connected to be energized bysaid ignition voltage, a resistor connected in series with saidcapacitor, the impedance of said capacitor being larger than theimpedance of said resistor whereby the amplitude of the current in saidseries circuit is determined principally by the impedance of saidcapacitor, and a contact making voltage responsive device connected inshunt with at least a portion of said resistor, said voltage responsivedevice being arranged to close its contacts upon the occurrence of apredetermined current in said resistor producing a predetermined voltagedrop thereacross.

9. An overspeed device for an engine having an ignition circuitproviding a pulsating voltage whose frequency is proportional to thespeed of the engine, comprising a capacitor and a potentiometer resistorhaving an adjustable intermediate terminal connected in series forenergization by said pulsating voltage, said capacitor having aconsiderably greater impedance than said resistor whereby the amplitudeof the current in said series circuit is approximately proportional tosaid frequency and said speed, a contact making voltage responsivedevice connected between the adjustable terminal and one fixed terminalof said potentiometer resistance, said voltage responsive device beingarranged to close its contacts upon the occurrence of a selected voltagedrop across said potentiometer resistor corresponding to a predeterminedcurrent through said resistor which corresponds to a predeterminedengine speed, and control circuit means responsive to the closing ofsaid contacts to deenergize said ignition circuit and stop the operationof said engine upon the occurrence of said predetermined speed.

References Cited in the file of this patent UNITED STATES PATENTS1,029,480 Tirrill June 11, 1912 2,010,960 Pogue Aug. 13, 1935 2,108,014Jones Feb. 8, 1938 2,161,146 Echlin et al. June 6, 1939 2,251,436Bentley et al. Aug. 5, 1941 2,301,115 Gilbert Nov. 3, 1942 2,349,992Schrader May 3, 1944 2,377,591 Taylor June 5, 1945

